PROJECT SUMMARY This is a FIRCA application for the collaboration between Dr. Nilgun Tumer at Rutgers University, New Brunswick, New Jersey and Dr. Marek Tchrzewski at the Maria Curie Sklodowska University in Poland. This research will be done at the Maria Curie Sklodowska University in Poland as an extension of NIH Grant No. R01-AI072425, 3-15-2007 to 2-29-2012. This collaboration makes use of the unique resources and research environment in Dr. Tchrzewski's lab to use ricin A chain (RTA) as a molecular tool to probe the function of the eukaryotic ribosomal stalk and to identify the functional part of the stalk structure. In spite of its fundamental importance in protein synthesis, the molecular architecture of the eukaryotic stalk and details of its function are not known due to the lack of appropriate molecular tools. Dr. Tchrzewski has developed the yeast strains and the methods to isolate the in vivo assembled eukaryotic ribosomal stalk for the first time. Isolation of the whole native stalk from yeast has revolutionized the method of stalk preparation and facilitated research on the function of the eukaryotic ribosomal stalk. Dr. Tumer has developed the model systems to study the activity of ricin A chain (RTA) and discovered that RTA binds to the ribosomal stalk to inhibit protein synthesis. In collaboration with Dr. Tchrzewski, Dr. Tumer showed direct interaction between RTA and the isolated native yeast ribosomal stalk, and obtained preliminary data demonstrating that RTA can be used as a very specific molecular tool to probe the structure and the function of the eukaryotic stalk. We propose to identify the stalk components critical for binding RTA, study the interaction of RTA with stalk complexes from different species, including bacteria, archaea, yeast and human and to identify the functional part of the stalk structure. This collaboration will connect the ongoing structure function analysis of RTA in the parent grant with biochemical, structural and genetic analysis of the stalk in Dr. Tchrzewski's lab in Poland and will provide new insights into the role of the ribosomal stalk in protein synthesis.